The present invention relates to a dot print head used in a serial dot printer, a printer having such a dot print head, a method of control over a printer, and a method of printing using such a control,
Impact type printers performing printing by impact on a printing medium with wires through ink ribbon are widely used, as output devices of information processing systems and the like, since they can be used for a variety of printing media, and they are relatively less costly.
The impact type printers can be divided into those of the spring-charge type, those of the plunger type, and those of the clapper type.
In a printer of the spring-charge type, an armature to which a wire is fixed is supported by a plate spring such that it can be swung, and the armature is normally attracted to a core by means of a permanent magnet, overcoming a resilient force of the plate spring, and printing is performed by energizing a coil wound on the core to create a magnetic flux opposing the magnetic flux of the permanent magnet, to thereby release the armature. As the demand for hither printing speed is increasing in recent years, printers having the dot print head of the spring-charge type having a high-speed response are widely used.
FIG. 1 is a side view showing an example of the structure of a dot print head of the spring-charge type in the prior art. In FIG. 1, the left half shows a section for illustrating the internal structure.
Referring to FIG. 1, a wire dot print head 1 is provided with an electrically conducting board 2 which is mounted to a rear surface of a base 3 via an insulating board, not shown.
Stacked in turn on the upper surface of the base 2 are a first yoke 4, a permanent magnet 5, a second yoke 6, and a spacer 7. These are integrated by means not shown.
Provided on the spacer 7 are a plate spring 8, a third yoke 9, an armature 10, a guide nose 11 and a guide frame 12, which are positioned by knock pins not shown and stacked in turn.
Disposed on the rear surface of the base 3 is a cap 14 with heat radiating fins 13 covering and protecting the printed circuit board 2.
The print head 11 is integrated by means of a clamp spring 16 which is engaged with the upper surface of the guide frame 12 and an engagement catch 15 of the cap 14.
More specifically, provided on the base 3 are electromagnets comprising coils 19 wound via coil bobbins 18 on the outer periphery of the cores 17, the electromagnets being provided in number corresponding to the printing wires 20, and arranged radially. The terminals 19a of the coils 19 extend out of the lower ends of the coil bobbins 18, and connected to the printed circuit board 2.
The plate spring 8 comprises flexible parts 8a supported in a cantilever fashion and protruding toward the center, and provided in number corresponding to the electromagnets and to confront the cores 17. Armatures 10 are mounted to the flexible parts 8a adjacent to the third yoke 9 and in confrontation with the cores 17 of the electromagnets 17.
Mounted to the tips of the armatures 10 are print wires 20, and the tips of the printing wires 20 are disposed slidably in the guide: holes in the wire guide fixed to the guide nose 11.
Each of the electromagnets 17, together with an armature 10 and a print wire 20 associated therewith form a printing element.
The dot print head is electrically coupled with a drive circuit 35, which controls the electric currents flowing through the coils 19, in accordance with the printing data supplied from a control circuit 36, and drive timing signals produced in the drive circuit 35. Specifically, each printing element is driven by causing an electric current to flow through the coil when printing by the particular printing element is to be effected.
The operation of the wire dot printing head 1 configured as described above will next-be described. In the print head 1, a magnetic circuit is formed by which the magnetic flux from the permanent magnet 5 passes through the second yoke 6, the spacer 7, the third yoke 9, the armature 10, the plate spring 8, the cores 17, the base 3, and the first yoke 4, and returns to the permanent magnet 5.
When the current is not made to flow (when the printing is not performed) by the action of the drive circuit 35, the armature 10 and the flexible parts 8a of the plate spring 8 are attracted to the core 17 by the magnetic flux generated from the permanent magnet 5, and the printing wires 20 are retracted in the guide nose 11. FIG. 1 shows such a state.
When an electric current is made to flow through the coil 19, a magnetic flux is generated in the direction opposite to the magnetic circuit, i.e., to cancel the magnetic flux of the permanent magnet 5. Then the force attracting the armature 10 to the core 17 is reduced, and the distortion energy stored in the plate spring 8 is released, and the flexible part 8a of the plate spring 8 is returned with the armature 10. The print wire 20 fixed to the tip of the armature 10 is protruded from the guide nose 11, and is impacted on printing medium 32 on a platen 33 via an ink ribbon 31. In this way, characters, graphic patterns and the like are printed.
After the armature 10 is released, the current to the coil 19 is interrupted. Then, the armature 10 together with the print wire 20 returning having impacted on the printing medium is attracted to the core 17, with the flexible part 8a being distorted. This completes one cycle of printing operation by one printing element.
A plurality of printing elements each comprising the armature 10, the print wire 20, the electromagnet for driving the print wire 20, and the like are arranged radially. With regard to the number of the printing elements, 9-pin heads having 9 printing elements for printing alphanumeric characters, and 24-pin heads having 24 printing elements for printing Chinese characters or for producing improved printing quality (higher printing density) are most frequently used.
Because of the large number of the elements, the guide holes of the wire guide 21 acting as guide elements for guiding the tips of the print wires 20 to predetermined positions, are arranged in two rows separated in the right-and-left direction by substantially 7.5/180 inches, with the guide holes of one row being shifted in the up-and-down direction by substantially 1/180 inches, so that the guide holes are generally arranged in a staggered manner, as shown in FIG. 2.
The two-row guide arrangement of a 24-pin head in the prior art had the following problems.
(1) For printing a large number of vertical lines, such as in the case of Chinese characters, it is necessary to drive a large number of print wires (pins) 20 simultaneously. In such an occasion, the magnetic flux from other printing wires interferes and cancels the magnetic flux. It is therefore necessary to increase the energy applied for producing the printing force. Tile result is the lower efficiency. The current value of each of the printing elements is instantly increased, so that the supply of power may be insufficient, causing a voltage drop and lowering of the printing force. PA1 (2) Next with regard to the arrangement of the printing elements, the marks P1, P2, P3 . . . , P24 in FIG. 3 denote the positions of the roots of the wires, and the marks c1, C2, C3 . . . C24 denote the positions of the guides (guide holes). As will be seen from FIG. 3, the positions of the roots of the printing wires 20 are arranged in an elongated circle, while the positions of the guides are arranged in two straight rows. Thus, the direction and distance are different between the wire root positions P1 to P24 and the guide positions C1 to C24. As a result, the wire side pressure and the wire stress are different from one print wire to another, and the friction force between the guide hole of the wire guide 21 and the print wire 20 differs from each other, and the frequency of friction, the printing time, the printing force and the like also differ. PA1 driving each of the printing elements for printing either at a reference timing which occurs once a standard printing cycle having a standard period, at a timing 1/4 of the standard period past said reference timing, at a timing half the standard period past said reference timing, or at a timing 3/4 of the standard period past said reference timing. PA1 providing a dot print head having a plurality of printing elements each having a printing wire arranged substantially in an elongated circle centered at a line parallel with the direction in which the printing elements are driven, and which is provided with a wire guide having guide elements for the respective printing wires for guiding tips of the printing wires to predetermined positions on a printing medium, wherein the guide elements are divided into at least four rows each extending in the direction orthogonal to a direction of spacing movement and orthogonal to a direction in which the printing wires extend, and distances between said rows are multiples of 1/240 inches; PA1 moving the dot print head in said direction of spacing movement relative to a printing medium; and PA1 driving each of the printing elements for printing either at a reference timing which occurs once a standard printing cycle having a standard period, at a timing 1/4 of the standard period past said reference timing, at a timing half the standard period past said reference timing, or at a timing 3/4 of the standard period past said reference timing.
From the view point of noise, for producing a given number of dots (the number of printing elements simultaneously driven multiplied by the printing frequency), it is known that the noise is smaller when the number of printing elements simultaneously driven is reduced and the frequency is increased.
To solve this problem, the arrangement in which the guide holes in the wire guide 21 are in the form of a rhombus as shown in FIG. 4, the arrangement in which the guide holes in the wire guide 21 are in four rows as shown in FIG. 5, and the like have been proposed and have been put to practical use, to realize reduction in energy and reduction in noises. The dimensions between the guide holes in the arrangement in FIG. 4 and FIG. 5 are as shown in FIG. 4 and FIG. 5, and the shift between the right and left is 1/2 pitch and the arrangement is in the staggered pattern.
The rhombic or four-row arrangement is effective where the density is low such as in the case of printing characters. However, where the density is higher as in the case of graphics or the like, the effect is reduced, and where the solid black printing where all the pins (print wires 20) are driven, no effect is obtained.
In terms of the printing density in the direction of the spacing movement, and of whether or not so called "quasi-printing" is also adopted, the following modes are typically used. Namely, 60 DPI.F, 120 DPI.Q, 120 DPI.F, 240 DPI.Q, 180 DPI.F, 360 DPI.Q, 80 DPI.F, 90 DPI.F Here, DPI is an abbreviation of dot per inch indicating the printing density or printing spatial frequency in the direction of the spacing movement. F denotes a full mode in which the drive of the printing elements is effected only at a certain preselected timing, called reference timings, which occurs only once in each printing cycle. Q denotes a quasi mode in which the drive of the printing elements is effected not only at the reference timing, but also at a half-shifted timing which is after the reference timing by half the standard period of the standard printing cycle. The drive for printing at the half-shifted timing is not effected when the drive for printing at the reference timing is effected in the same printing cycle. The drive for printing at the reference timing is not effected when the drive for printing at the half-shifted timing is effected in the preceding printing cycle.
In one type of printers, the drive for printing is effected at the reference timing or the half-shifted timing. When drive for printing is effected with such printers in 60 DPI.F, 120 DPI.Q, 120 DPI.F, 240 DPI.Q, 180 DPI.F and 360 DPI.Q, which are frequently employed, to print solid black, all the printing elements may be simultaneously driven.
In an alternative arrangement where the guide holes of the printing elements are shifted and the generation of the printing timings must be adjusted for each of the various DPI modes, the control over the drive timings is complicated, and the circuitry for implementing such a control is expensive,